public abstract Class Lexer

Currently does not support multiple emits per nextToken invocation for efficiency reasons. Subclass and override this method and nextToken (to push tokens into a list and pull from that list rather than a single variable as this implementation does).

The standard method called to automatically emit a token at the outermost lexical rule. The token object should point into the char buffer start..stop. If there is a text override in 'text', use that to set the token's text. Override this method to emit custom Token objects. If you are building trees, then you should also override Parser or TreeParser.getMissingSymbol().

What is the index of the current character of lookahead?

Returns the EOF token (default), if you need to return a custom token instead override this method.

Overrides org.antlr.runtime.BaseRecognizer.getErrorMessage.

Doc from org.antlr.runtime.BaseRecognizer.getErrorMessage.

What error message should be generated for the various exception types? Not very object-oriented code, but I like having all error message generation within one method rather than spread among all of the exception classes. This also makes it much easier for the exception handling because the exception classes do not have to have pointers back to this object to access utility routines and so on. Also, changing the message for an exception type would be difficult because you would have to subclassing exception, but then somehow get ANTLR to make those kinds of exception objects instead of the default. This looks weird, but trust me--it makes the most sense in terms of flexibility. For grammar debugging, you will want to override this to add more information such as the stack frame with getRuleInvocationStack(e, this.getClass().getName()) and, for no viable alts, the decision description and state etc... Override this to change the message generated for one or more exception types.

Annotations

@Override

Implements abstract org.antlr.runtime.BaseRecognizer.getSourceName.

Implements org.antlr.runtime.TokenSource.getSourceName.

Doc from org.antlr.runtime.TokenSource.getSourceName.

Where are you getting tokens from? normally the implication will simply ask lexers input stream.

Annotations

@Override

Return the text matched so far for the current token or any text override.

This is the lexer entry point that sets instance var 'token'

Implements org.antlr.runtime.TokenSource.nextToken.

Return a token from this source; i.e., match a token on the char stream.

Lexers can normally match any char in it's vocabulary after matching a token, so do the easy thing and just kill a character and hope it all works out. You can instead use the rule invocation stack to do sophisticated error recovery if you are in a fragment rule.

Overrides org.antlr.runtime.BaseRecognizer.reportError.

Doc from org.antlr.runtime.BaseRecognizer.reportError.

Report a recognition problem. This method sets errorRecovery to indicate the parser is recovering not parsing. Once in recovery mode, no errors are generated. To get out of recovery mode, the parser must successfully match a token (after a resync). So it will go: 1. error occurs 2. enter recovery mode, report error 3. consume until token found in resynch set 4. try to resume parsing 5. next match() will reset errorRecovery mode If you override, make sure to update syntaxErrors if you care about that.

Annotations

@Override

Overrides org.antlr.runtime.BaseRecognizer.reset.

Doc from org.antlr.runtime.BaseRecognizer.reset.

reset the parser's state; subclasses must rewinds the input stream

Annotations

@Override

Set the char stream and reset the lexer

Set the complete text of this token; it wipes any previous changes to the text.

Instruct the lexer to skip creating a token for current lexer rule and look for another token. nextToken() knows to keep looking when a lexer rule finishes with token set to SKIP_TOKEN. Recall that if token==null at end of any token rule, it creates one for you and emits it.